Method of coal liquefaction

Abstract: A method of coal liquefaction comprising the steps of: (a) producing a coal slurry from a pulverized coal and a solvent;(b) compressing a coke oven gas to prepare a compressed gas; (c) reacting the coal slurry with the compressed gas in a reactor under a high pressure and high temperature condition to form a liquefied product; (d) separating the liquefied product into a used gas and a liquefied slurry; and (e) distillating the liquefied slurry to form a liquefied oil and a solvent refined coal.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates to a method of coal liquefaction. 2. DESCRIPTION OF THE PRIOR ART Fig. 4 shows a schematic flowchart of conventional method of coal liquefaction. According to the conventional method, a pulverized coal and a coal liquefied oil (solvent) obtained from the distillation step described later are charged into the slurry tank 2, where they are mixed together under agitation to prepare a coal slurry. The coal slurry is pressurized and mixed with a gas (recycle hydrogen gas) consisting mainly of hydrogen which was separated in the gas purifying step described later, and they are introduced to the heating furnace 3. The coal slurry entered into the heating furnace 3 is brought into a state of 1.01 x 10 7 Pa (100 atm) or more and 400 °C or more, and fed to the coal liquefaction reactor 4. The coal liquefaction reactor 4 conducts a liquefaction reaction under a hydrogen positive pressure and at an elevated temperature. The product of the liquefaction reaction leaving from the reactor 4 enters into the gas separator 6 where the product is separated to a gas and a liquefied slurry containing liquefied oil and non-liquefied matter. The liquefied slurry contains lots of ash and non-liquefied matter consisting mainly of un-reacted organic residue. Since those non-liquefied matter induces troubles in the succeeding treatment such as distillation, the liquefied slurry is sent to the filter 30 to separate the non-liquefied matter. The liquefied solution free of non-liquefied matter is sent to the distillation unit 8 to fractionate into light oil and fuel oil, and to recover the liquefied oil. A part of the liquefied oil is charged to the slurry tank 2 as the solvent for preparing coal slurry. The filter cake separated at the filter 30 is sent to the hydrogen manufacturing facility 31 as the raw material for hydrogen production, and is gasified there. On the other hand, the gas separated in the gas separator 6 is sent to the gas purification unit 7 for purification. Since the gas consists mainly of hydrogen, the gas is recycled and is added to the coal slurry which is fed to the liquefaction reactor 4. However, solely the hydrogen recycled is not sufficient to carry the liquefaction reaction, the hydrogen obtained by gasification of the filtrate discharged from the hydrogen manufacturing facility 31 is added to the coal slurry. The hydrogen manufacturing facility 31 consists of many treatment stages including the gasification stage where the filtrate is completely decomposed under the presence of oxygen, the purification stage for purifying the generated decomposed gas, the hydrogen-enriching stage where the CO gas in the generated gas is shift-reacted to yield a hydrogen-rich gas, the gas cooling stage, and the stage for CO 2 removal from the gas using alkali. In this manner, the hydrogen manufacturing facility becomes very complex one. According to the above-described method, the liquefaction reaction has to use hydrogen which is produced in an extremely complex hydrogen manufacturing facility 31. Since the hydrogen manufacturing facility 31 is very complex one, it is expensive (as high as nearly 40% of the total investment of the liquefaction plant, in some cases), as well as expensive operating cost. Therefore, the share of hydrogen manufacturing cost to the total coal liquefaction product cost becomes very high. DE-A-27 11 105 discloses a method of coal liquefaction which comprises forming a coal slurry from pulverized coal and a solvent; reacting the coal slurry with a gas in a reactor at high pressure and temperature to form a liquefied product; separating reacted gas from the liquefied product to form a liquefied slurry; coking the liquefied slurry; and distilling the liquefied slurry to form a liquid oil and solvent-refined coal. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of coal liquefaction which allows to significantly reduce the cost of coal liquefied products. To achieve the object, the present invention provides a method of coal liquefaction comprising the steps of: (a) producing a coal slurry from pulverized coal and a solvent; (b) reacting the coal slurry with hydrogen-containing coke oven gas in a reactor at a pressure of 1.01 × 10 7 Pa (100 atm) or more and a temperature of 400°C or more to form a liquefied product, the coke oven gas being generated during the carbonization of coal in a coke oven, (c) separating the liquefied product into a used gas and a liquefied slurry; and (d) distillating the liquefied slurry to form a liquefied oil and a solvent refined coal; characterized in that the hydrogen-containing coke oven gas is compressed by employing the energy of the used gas prior to introducing it into the reactor. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic flowchart of an example of the present invention; Fig. 2 is a schematic flowchart of another example of the present invention; Fig. 3 is a schematic flowchart of further example of the present invention; and Fig. 4 is a schematic flowchart of a conventional coal liquefaction process. DESCRIPTION OF THE PREFERRED EMBODIMENT Based on a series of extensive investigation and experiments, the inventors found that the liquefaction reaction satisfactorily proceeds even a coke oven gas is used as the hydrogen source. Coke oven gas is a gas which is generated during carbonizing a coal in the coke oven. The coke oven gas contains hydrogen and methane as main component. The coke oven gas is hereinafter referred to simply as "COG". Accordingly, this invention uses COG as the hydrogen source and, after completing the liquefaction reaction, the used COG is returned to the COG supply system instead of recycling the COG. In this case, the used COG under a high pressure is introduced to the gas expander to recover the high pressure energy for utilizing it as the compression power source of COG being supplied for liquefaction reaction. The energy recovery allows a significant reduction of the power supply for COG compression. Since the temperature of liquefied product leaving the reactor is 400°C or more, the process of this invention provides a step of recovering the heat of the liquefied product and a step of preheating the coal slurry using the recovered heat for reducing the supply of heat. Furthermore, a pre-treatment of coal is conducted to reduce ash content. The ash removal prevents accumulation and adhesion of ash in process facilities, and reduces troubles on operation caused from the ash accumulation and adhesion. The pre-treatment of coal is what is called the oil agglomeration method. According to the method, a coal-water slurry is prepared either by adding water to a pulverized coal or by pulverizing a coal after adding water to it. When the coal-water slurry is mixed with an oil (liquefied oil), the coaly components and the oil bind together to form pellets, which pellets are then separated from aqueous phase. Ash in the coal is left in the aqueous phase. Consequently, a mixture consisting mainly of coaly components and oily components is separated from a mixture consisting mainly of ash and water. In this simple manner, ash is removed from coal. EXAMPLE Fig. 1 illustrates an example of this invention. The same functional units and equipment with those in Fig. 4 have the same reference number in both figures, and their description is not given. According to the example, COG is supplied as the hydrogen source for conducting liquefaction reaction. COG supplied from the COG supply system is introduced to the methane converter 20, then to the shift reactor 21, where COG is modified to a hydrogen-rich gas. The modification of COG is performed by the following procedure. In the methane converter 20 as the first stage, both COG which was desulfurized in advance and steam are introduced, and the reaction between them is conducted at approximately 850 °Cand under approximately 2.03MPa (20 atm), and under the presence of a catalyst, (equation (1)), where the methane in COG is converted to hydrogen and carbon monoxide. This reaction increases the hydrogen concentration in COG. CH 4 + H 2 O = 3H 2 + CO The gas after the reaction is sent to the waste heat boiler (not shown) where the gas is cooled to approximately 400 °C. In the shift reactor 21 as the second stage, the gas reacted in the first stage and cooled in the waste heat boiler is introduced, and the reaction, equation (2), is conducted under the presence of a catalyst. CO + H 2 O = H 2 + CO 2 The gas generated from the second reaction is cooled near to room temperature to remove moisture. Since the above-described reactions increase the hydrogen content of the gas, the required amount of COG to supply to the liquefaction reaction is reduced, and the COG compression power is reduced. The modified COG is compressed by the compressor 22, and is added to the coal slurry pumped out from the slurry tank 2. The coal slurry containing COG is adjusted to the pressure of 1.01 × 10 7 Pa (100 atm) and the temperature of 400 °C or more in the heating furnace 3, then the slurry is fed to the reactor 4. In the reactor 4, the liquefaction reaction is carried out to convert the coal slurry into gas and liquefied slurry which is a mixture of liquefied oil and non-liquefied matter. The liquefied products are fed to the gas separator 6. In the gas separator 6, the liquefied product is separated to the used COG and the liquefied slurry. The liquefied slurry is then fed to the distillation unit 8 without filtered and at a state containing ash. A part of the liquefied oil distilled from the distillation unit 8 is recycled to the slurry tank 2, and the rest of the liquefied oil distillate is recovered as light oil. The residue containing ash is recovered as the product consisting mainly of solvent refined coal (SRC), which residue is useful as a caking additive for producing high quality coke or the like. The used COG separated at the gas separator 6 is purified in the gas purification unit 7, and is withdrawn to the outside of the system without recycling to the reaction system. The withdrawn used COG has a pressure of 1.01 × 10 7 Pa (100 atm), so it is introduced to the gas expander 23 connected to the compressor 22 to drive it. The used COG discharged from the gas expander 23 is reduced its pressure near to atmospheric pressure, returned to the COG supply system, and used in a common applications such as fuel gas and raw material for chemicals. This example deals with the case of supplying COG which was modified to a hydrogen-rich state as the hydrogen source. Nevertheless, this invention not necessarily requires this type of modification, and ordinary COG may be supplied directly. As described above, since this example supplies COG as the hydrogen source, hydrogen production is not necessary, and no hydrogen production facility to gasify the un-reacted residue is needed. Fig. 2 illustrates another example of this invention. The same functional units and equipment with those in Fig. 1 have the same reference number in both figures, and their description is not given. According to the example, The coal slurry being fed to the heating furnace 3 is preheated by the recovered heat of the reaction system. To do this, a heat exchanger 5a for preheating and a heat exchanger 5b for heat recovery are installed at the upstream of the heating furnace 3 and the downstream of the liquefaction reactor 4, respectively. The coal slurry withdrawn from the slurry tank 2 is preheated by the heat exchanger 5a and is fed to the heating furnace 3, then to the liquefaction reactor 4. The temperature of reaction product discharged from the liquefaction reactor 4 is 400 °C or more. The reaction product is passed through the heat exchanger 5b to perform the heat recovery, then the product is sent to the gas separator 6. A passage of recycling an organic heating medium is located between the heat exchanger 5a and the heat exchanger 5b. The heating medium which was heated by the reaction product having a high temperature in the heat exchanger 5b is sent to the heat exchanger 5a where the heating medium heats the coal slurry sent from the slurry tank 2. Fig. 3 illustrates further example of this invention. The same functional units and equipment with those in Fig. 1 and Fig. 2 have the same reference number in both figures, and their description is not given. According to the example, a pre-treatment of coal is conducted to eliminate ash in the coal. To do this, the ash separator 1 is installed at the upstream of slurry tank 2 which prepares the coal slurry. In the ash separator 1, water is added to the pulverized coal to prepare a coal-water slurry. Then, the liquefied oil obtained from the distillation unit 8 is mixed to the slurry. The liquefied oil mixing induces the binding of coaly components in coal into the liquefied oil to form a mixture of pellet shape. The pellet shaped mixture is separated by sieving, and is sent to the slurry tank 2. The ash components remain in the slurry and are removed at the sieving treatment. In the slurry tank 2, the liquefied oil obtained in the distillation unit 8 is added to the coaly pellet shaped mixture under agitation to prepare the coal slurry. EXAMPLE 1 A coal for general use was liquefied following the method illustrated in Fig. 1. A common COG without treating for hydrogen-enriching was used as the hydrogen source. A coal for general use (pulverized to -80mesh 100%, and containing ash of 8.26% and water of 2.75% by dry weight base) was charged to the slurry tank 2 at a rate of 112 kg/hr. The liquefied oil was added to the tank at a rate of 150 kg/hr. Those components were mixed under agitation to prepare a coal slurry. The coal slurry was pressurized to 1.01 × 10 7 Pa (100 atm). COG (having the composition listed in Table 1) pressurized to 1.01 × 10 7 Pa (100 atm) was added to the slurry, then the mixture was heated and sent to the liquefaction reactor 4. COG was further added to the mixture at a rate of 65 Nm 3 /hr, and the liquefaction reaction was carried out at 430 °C and residence time of approximately 20 min. The product of the liquefaction reaction was sent to the gas separator 6 where the used COG and the liquefied slurry were separated each other. The liquefied slurry was sent to the distillation unit 8 for fractionation. In the example, COG was used as the hydrogen source. The liquefaction reaction proceeded in a similar manner as in the case that hydrogen was used. From the light oil (liquefied oil) of 166kg distilled from the distillation unit 8, 16kg was obtained as the product. The product recovered from the bottom of the distillation uit 8 was 79kg, which contained SRC of 82.7%, un-dissolved organic matter of 5.9%, and ash of 11.3%. H 2 CH 4 C 2 H 4 CO CO 2 N 2 56 28 3 7 3 3 ( vol.% ) EXAMPLE 2 A coal was liquefied following the process shown in Fig. 2, where the coal slurry was preheated. The coal slurry was prepared with the coal for general use employed in Example 1 at a rate of 112 kg/hr. The liquefaction reactor 4 was operated in the similar manner as in Example 1 under the reaction condition of 430°C, 1.01 × 10 7 Pa (100 atm), and residence time of approximately 20min. The heating medium for heat exchanger was a mixture of diphenyl and diphenylether, which was recycled at a rate of 300 kg/hr. The reaction product (248 kg/hr) discharged at 430 °C from the reaction tower 4 exchanged heat with the heating medium in the heat exchanger 5b to raise the temperature of the heating medium to 350°C . The heated heating medium exchanged its heat with the coal slurry (80°C, 262 kg/hr) in the heat exchanger 5a to raise the temperature of the coal slurry to 280°C. The heating medium which lost the heat and reduced its temperature to 167°C was recycled to the heat exchanger 5b. The heat recovery conducted in the example reduced the necessary heating temperature range from 350°C (80°C to 430 °C in a conventional process) to 150°C (280 °C to 430 °C). The effect of heat recovery reduced the heat required to raise the coal slurry temperature by 50 to 60% compared with conventional process. EXAMPLE 3 A coal for general use was liquefied following the process given in Fig. 3 using a coal removed its ash in advance. The coal slurry was prepared in the following procedure for removing the ash therefrom. Water of 330kg/hr was added to a coal for general use (containing ash of 10% and water of 7.6% by dry weight base) of 130 kg/hr. The mixture was pulverized to obtain the coal-water slurry. The size of pulverized coal was -80mesh 100%. The coal-water slurry was charged to the ash removal unit 1 where the liquefied oil of 11 kg/hr was added to mix together and where the mixture was separated into coaly components and ash. The mixture of coaly components was granules of 1 to 3mm in size and consisted of coaly components of 100 kg/hr, ash of 2 kg/hr, and liquefied oil of 10 kg/hr. The residue was a mixture of ash of 10 kg/hr, coaly components of 8 kg/hr, liquefied oil of 1 kg/hr, and water of 337 kg/hr. The mixture of the coaly component side was charged to the slurry tank 2 to mix with the added liquefied oil of 140 kg/hr under agitation to prepare the coal slurry. The prepared coal slurry was treated by liquefaction reaction under the same condition with Example 1. The reaction product of the liquefaction reaction was introduced to the gas separator 6 to separate it into used COG and liquefied slurry. The liquefied slurry was sent to the distillation facility 8 for distillation. The process drastically reduced the frequency of cleaning of the process facilities to remove adhered and deposited non-liquefied matter compared with the frequency in conventional process. EXAMPLE 4 A COG (composition is given in Tale 2) and steam were introduced to the methane conversion unit 20 at a rate of 800 Nm 3 /hr and 36 kg/hr, respectively to react them under the condition of 2.03 MPa (20 atm), 850 °C, presence of a catalyst. The gas generated from the reaction had the flow rate of 1550 Nm 3 /hr and its composition is given in Table 2 (the reacted gas at the first stage). The reacted gas was introduced to the waste heat boiler to cool to 400 °C, then it was sent to the shift reactor 21 to conduct the second reaction under 2.03 MPa (20 atm) and under the presence of a catalyst. The yielded gas was 1350 Nm 3 /hr and its composition is given in Table 2 (the reacted gas at the second stage). The reacted gas was cooled to 30°C, and a part of the gas was supplied for the liquefaction reaction. The modified COG used in the liquefaction reaction, when compared the composition excluding water content, increased its hydrogen concentration by approximately 17%. Accordingly, the necessary amount of COG reduced to approximately 79% compared with the case of non-modified COG application, and the required power for compression COG also reduced to that level. In addition, the cooling of reacted gas by the waste heat boiler generated steam of 1.0 MPa (10 kgf/cm 2 ) at a rate of 456 kg/hr. Coke Oven Gas First Stage Second Stage H 2 53.6 52.6 62.0 CH 4 26.8 10.1 10.1 C 2 H 4 2.9 CO 7.6 11.8 2.4 CO 2 1.9 1.9 11.3 N 2 2.9 1.5 1.5 H 2 O 4.3 22.1 12.7 ( vol.% ) EXAMPLE 5 The power required to raise the pressure of COG in Example 4 was 119 kw. The gas after the second state reaction was compressed to 100 atm to feed the coal liquefaction reaction step. The consumed power at that compression was 104 kw. To recover the power from the gas coming from the coal liquefaction reactor, the reacted gas was heated to 150 °C with the steam obtained in Example 4, and the three stage gas expander was employed. The resulted recovered power was 130 kw. The total power recovery rate was 58%. The final gas volume was 1038 Nm 3 /hr. According to the invention, a considerably inexpensive COG is used as the hydrogen source for the coal liquefaction reaction, so the production cost of liquefied oil and SRC is significantly reduced. Furthermore, the used COG is introduced to the gas expander, and the pressure energy of COG is recovered as an auxiliary power source of compressor, which saves the power consumption for compressing COG by 50% or more compared with a conventional process and which contributes to the cost reduction. When the heat of high temperature liquefied oil is recovered by contacting it with a heating medium in a heat exchanger, and when the recovered heat is used to preheat the coal slurry, the required additional heat to heat the coal slurry decreases to approximately 50 to 60% and the heating cost reduces to that amount. When the ash in coal is removed and when the ash-free coal is introduced to the liquefaction reaction step, the troubles of ash accumulation and adhesion in the process facilities drastically diminish, and the cost accompanied with turn down reduces.

Claims: A method of coal liquefaction comprising the steps of: (a) producing a coal slurry from pulverized coal and a solvent; (b) reacting the coal slurry with hydrogen-containing coke oven gas in a reactor at a pressure of 1.01 x 10 7 Pa (100 atm) or more and a temperature of 400°C or more to form a liquefied product, the coke oven gas being generated during the carbonization of coal in a coke oven, (c) separating the liquefied product into a used gas and a liquefied slurry; and (d) distillating the liquefied slurry to form a liquefied oil and a solvent refined coal; characterized in that the hydrogen-containing coke oven gas is compressed by employing the energy of the used gas prior to introducing it into the reactor. A method according to Claim 1, wherein the conversion of the energy of the used gas to mechanical work is conducted by a gas expander. A method according to Claim 1 or Claim 2, further comprising the step of pre-heating the coal slurry by exchanging heat between the coal slurry prepared in step (a) with the liquefied product formed in step (b). A method according to any preceding Claim, wherein the coal slurry is produced by the steps of: adding water to pulverized coal to produce a coal-water slurry; mixing a liquid oil with the coal-water slurry; separating the oil-slurry mixture into (A) coal components and liquefied oil, and (B) a mixture of ash and water; and further adding a liquid oil to the mixture (A) to form the coal slurry. A method according to any preceding Claim, further comprising the steps of upgrading the coke oven gas by: reacting coke oven gas with steam in the presence of a catalyst; and reacting the CO in the resulting gas with H 2 O to yield H 2 and CO 2 to increase the hydrogen content of the coke oven gas.

Inventors: MATSUBARA KENJI, MOCHIDA TSUNEAKI, SUZUKI NOBUO, MATSUBARA, KENJI, MOCHIDA, TSUNEAKI, SUZUKI, NOBUO, Mochida, Tsuneaki, c/o NKK Design &amp; Engin. Corp., SUZUKI, NOBUO, C/O INTELLECTUAL PROPERTY DEPT.
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1994
Main classification: C10G1
IPC codes: C10G1